1. Field of the Invention
The present invention relates to projection apparatus that employ image forming devices such as DMD (Digital Micro-mirror Device), in particular, to a configuration of adjusting an irradiating region for irradiating the light from a light source to the image forming device.
2. Description of the Related Art
FIG. 1 is a view showing a schematic configuration of a projector 100 of DLP (Digital Light Processing) type. The projector 100 is one example of the projection apparatus. An illustrated image projection optical system unit is arranged inside the main body 1 of the projector 100. An air conditioning system unit, a controlling system unit, a power supply system unit etc. (not shown) are also arranged inside the main body 1.
Reference numeral 3 is a lamp serving as a light source, 4 is a reflector, and 2 is a lamp case for holding the lamp 3 and the reflector 4. Reference numeral 5 is a color wheel made of circular disc in which the color filters of red, green and blue are alternately arranged in the circumferential direction. The color wheel 5 that is rotated by a motor (not shown) transmits the white light emitted from the lamp 3 through one of the color filters, and separates the white light to red light, green light and blue light. Reference numeral 6 is an engine casting or a vertically separable frame made of magnesium. Components 7 to 11 of the image projection optical system described below are respectively assembled to the engine casting 6. Reference numeral 7 is a light tunnel of square tube shape having a mirrored inner surface. The light entered from an incident port 7a, which is an opening on one end side, is repeatedly reflected in the inside of the light tunnel 7, and exit from an exit port 7b, which is an opening on the other end side, thereby changing the light to a condensed uniform light in a short light path. Reference numeral 8 is a mirror for reflecting the light that has passed through the light tunnel 7. The light path length is shortened and the image projection optical system is miniaturized through the use of the light tunnel 7 and the mirror 8. Reference numeral 9 is a relay lens for aligning the light flux of the light reflected by the mirror 8.
Reference numeral 10 is a DMD (Digital Micro-mirror Device) in which several hundred thousand microscopic micro-mirrors (not shown) are integrated on a semiconductor memory, where each micro-mirror assigned with the memory cell configures the pixel. The DMD 10 is one example of the image forming device and is mounted on a circuit board (not shown) The micro-mirror of the DMD 10 that can be tilted in two directions at ±12° tilts to one direction by the electrostatic attraction force according to the memory value, and takes a binary state of ON/OFF depending on the tilted direction. Reference numeral 11 is a projection lens made up of a tube that is compressible in the axis direction, and a plurality of lenses etc. equipped inside of the tube. The projection lens 11 passes the light reflected by the DMD 10 and projects the light onto the screen 50.
As shown with an arrow, the white light emitted from the lamp 3 is passed through the opening 2a of the lamp case 2, passed through one of the color filters of the color wheel 5, and separated to the red light, green light and blue light. Each color light enters the inside through the opening 6a of the engine casting 6, and passes through the light tunnel 7 to be condensed and uniformed. The light exit from the light tunnel 7 is passed through the lower side of the projection lens 11, reflected upward at a predetermined angle by the mirror 8, passed through the relay lens 9, and irradiated onto the DMD 10. In this case, when the micro-mirror of the DMD 10 is in the ON state, the light reflected by the mirror is taken into the projection lens 11 and projected onto the screen 50. When the micro-mirror is in the OFF state, the light reflected by the mirror is not taken into the projection lens 11, and thus is not projected onto the screen 50. That is, the projector 100 forms the image with the DMD 10 by ON/OFF controlling the operation state of each micro-mirror of the DMD 10 based on the input video signal and the like, and projects the image onto the screen 50 through the projection lens 11.
FIG. 14 is a view showing a conventional irradiating state of the light on the DMD 10. Rectangle 10a shown with a solid line is the image forming surface of the DMD 10 arranged on the side to be irradiated with light. The image forming surface 10a consists of above-described micro-mirrors. The light emitted from the lamp 3 is passed through the light tunnel 7 and the like, reflected by the mirror 8, and irradiated onto the DMD 10, as described above. In this case, the light is narrowed according to the diameter of the light tunnel 7 of square tube shape, and the light path is bent by the reflection at the mirror 8, and thus the irradiating region of the light irradiated on the DMD 10 becomes a square shape tilted (sometimes deformed) with respect to the image forming surface 10a as shown with 10b in a dot-dash line in FIG. 14, and the light may not be irradiated to one part, as indicated by the shaded area, of the image forming surface 10a. If the image is formed with the DMD 10 and projected onto the screen 50 in this state, the image quality may degrade such as the projected image may become dark.
Therefore, the attachment angle and position of the mirror 8 with respect to the engine casting 6 have been adjusted in the prior art to adjust the irradiating region of the light on the DMD 10 so that light is irradiated to the entire image forming surface 10a. Furthermore, the irradiating region of the light on the DMD 10 sometimes cannot be adequately adjusted so that light is irradiated on the entire image forming surface 10a only by adjusting the attachment of the mirror 8, in which case, the size of the diameter of the light tunnel 7 is changed to larger size, which enlarges the irradiating region of the light to 10c, as shown with a dot-dot-dash line in FIG. 14, in the prior art. However, the optical specification must be changed if the size of the light tunnel 7 is changed, which leads to adverse effects such as lowering in energy of the light per unit area to be irradiated on the DMD 10, and re-designing etc. of the image projection optical system may become necessary, which is very troublesome. Furthermore, various light tunnels 7 of different sizes must be manufactured and prepared, which is very costly.
Patent document 1; Japanese Patent Application Laid-Open No. 2000-155373 discloses a technique of adjusting the image displaying position on the screen by arranging a motor for rotating the projection lens with the optical axis as the center, a motor for operating a zoom mechanism of the projection lens, and a motor for moving a liquid crystal panel, DMD etc. in the X direction perpendicular to the optical axis and the Y direction in a rear projection television etc., and operating each motor through switch operation. However, such technique is difficult to apply to the adjustment of the irradiating region of the light on the DMD 10, and is also costly since a great number of motors and switches are used.